Engine running bad at idle

I think the idle, in gear, should be about 750 rpm, definitely not 900. If you are looking at the tachometer, it isn't that accurate visually. a scanner should be connected to get an accurate reading. A little vibration at idle is not abnormal. But you might try adjusting the engine mounts to eliminate it.

my guess, car unseen.
car has an A/T trans, and all A/T jump from park to drive
selection is made on a cold engine, due to the very fast idle speed.
what was the park and cold idle speed. and out door temps.
the lower out door temps, make idle speed , cold engine, even higher
but when the engine reaches 180F or more and holds, the RPM
is about 800 RPM (the FSM tells the exact amount and does vary for the unstated engine option) so at 800 the tranny don;t lurch, did it on a hot engine. so if idle speeds are wrong say so and say it with engine temps. or its all meaningless.
next :
runs rough, the engine (even parked?) is called misfire.
misfire on a good engine (full compression)
is:
1: bad spark (or never had a tune up ever) every 60k miles.
2: bad fueling. too rich, too lean (low idle) bad injectors (stuck or clogged, or wrong fuel pump pressure or bad Fuel pressure regulator)
3: bad fuel.

there is a test for each possible failure. all very simple test.
it takes $80 in gauge tools to find engine problems.

idle speed too low, idle speed 900 - 950 rpm for the 2.5 engine and 750 rpm for the 3.9 engine.check for a vacuum leak at pcv valve make sure it is in place in valve cover.

This IAC valve runs only when your foot is off the gas pedal. Mainly to keep the engine from stalling and keeping it at a safe RPM. If it is running bad under 2000RPM, more than likely its the IAC valve or a vacuum leak. Clean or replace the IAC valve....Hopefully this helps!!

You don't need to change the spark plugs since it has only 31.5 K. The plugs should last 60K. There is a an adjustment at the gas cable end at engine to increase the idle a little bit. You can increase rpm at idle to 600 RPM. Since your RPM at idle is low that why it is shaking at idle, red lights. Let me know it it is shaking at high speed ( 2500 RPM)

check for lose vacuum hoses or lose throttle hose make sure you air flow meter ducks are tite if you see everything ok then the idle speed control valve could be dirty with a little carburetor cleaner spray while engine is running open throttle and spray into throttle till you can see throttle is clean you may have to do this a few time hope this information is useful good luck

From the service manual:

Idle Speed/Ignition Timing/Idle Mixture Ratio Adjustment
NGEC0549
PREPARATION
NGEC0549S01
1) Make sure that the following parts are in good order.
I Battery
I Ignition system
I Engine oil and coolant levels
I Fuses
I ECM harness connector
I Vacuum hoses
I Air intake system
(Oil filler cap, oil level gauge, etc.)
I Fuel pressure
I Engine compression
I EGR valve operation (If so equipped)
I Throttle valve
I Evaporative emission system
2) On air conditioner equipped models, checks should be carried out while the air conditioner is OFF.
3) On automatic transmission equipped models, when checking idle rpm, ignition timing and mixture ratio,
checks should be carried out while shift lever is in “N” position.
4) When measuring “CO” percentage, insert probe more than 40 cm (15.7 in) into tail pipe.
5) Turn off headlamps, heater blower, rear defogger.
6) Keep front wheels pointed straight ahead.
7) Make the check after the cooling fan has stopped.

SEF976U
3. Open engine hood and run engine at about 2,000 rpm for about 2 minutes under no-load.
SEF977U
4. Perform diagnostic test mode II (Self-diagnostic results). Refer to EC-644.
SEF217U
OK or NG
OK ' GO TO 2.
NG ' 1. Repair or replace components as necessary.
2. GO TO 2.
BASIC SERVICE PROCEDURE VG33E
Idle Speed/Ignition Timing/Idle Mixture Ratio Adjustment (Cont’d)
EC-616
2 CHECK IGNITION TIMING
1. Run engine at about 2,000 rpm for about 2 minutes under no-load.
2. Rev engine (2,000 to 3,000 rpm) two or three times under no-load, then run engine at idle speed.
SEF978U
3. Turn off engine and disconnect throttle position sensor harness connector.
SEF975R
4. Start and rev engine (2,000 - 3,000 rpm) two or three times under no-load, then run at idle speed.
5. Check ignition timing with a timing light.
SEF371S
15°±2° BTDC (in “P” or “N” position)
OK or NG
OK ' GO TO 4.
NG ' GO TO 3.
GI
MA
EM
LC
FE
CL
MT
AT
TF
PD
AX
SU
BR
ST
RS
BT
HA
SC
EL
IDX
BASIC SERVICE PROCEDURE VG33E
Idle Speed/Ignition Timing/Idle Mixture Ratio Adjustment (Cont’d)
EC-617
3 ADJUST IGNITION TIMING
1. Adjust ignition timing by turning distributor after loosening securing bolts.
2. Turn off engine and connect throttle position sensor harness connector to throttle position sensor.
SEF972R
' GO TO 2.
4 CHECK BASE IDLE SPEED
With CONSULT-II
1. Read idle speed in “DATA MONITOR” mode with CONSULT-II.
PEF356V
700±50 rpm (in “P” or “N” position)
Without CONSULT-II
1. Check idle speed.
700±50 rpm (in “P” or “N” position)
OK or NG
OK ' GO TO 6.
NG ' GO TO 5.

Since this is an intermittent problem, first try to determine if the problem arises due to one of these many intermittent problems:

* Vehicle vibration
* Heat sensitive
* Freezing
* Water intrusion
* Electrical load
* Cold or hot start up

If you can't isolate the cause of the intermittent problem, you can try adjusting the Idle Speed/Ignition Timing/Idle Mixture Ratio:

Idle Speed/Ignition Timing/Idle Mixture Ratio Adjustment

PREPARATION
1) Make sure that the following parts are in good order.

* Battery
* Ignition system
* Engine oil and coolant levels
* Fuses
* ECM harness connector
* Vacuum hoses
* Air intake system
* (Oil filler cap, oil level gauge, etc.)
* Fuel pressure
* Engine compression
* EGR valve operation (If so equipped)
* Throttle valve
* Evaporative emission system

2) On air conditioner equipped models, checks should be carried out while the air conditioner is OFF.
3) On automatic transmission equipped models, when checking idle rpm, ignition timing and mixture ratio,
checks should be carried out while shift lever is in “N” position.
4) When measuring “CO” percentage, insert probe more than 40 cm (15.7 in) into tail pipe.
5) Turn off headlamps, heater blower, rear defogger.
6) Keep front wheels pointed straight ahead.
7) Make the check after the cooling fan has stopped.

INSPECTION PROCEDURE

1 INSPECTION START
1. Visually check the following:
I Air cleaner clogging
I Hoses and ducts for leaks
I EGR valve operation (If so equipped)
I Electrical connectors
I Gasket
I Throttle valve and throttle position sensor operation
2. Start engine and warm it up until engine coolant temperature indicator points to the middle of gauge.
Ensure engine stays below 1,000 rpm.
3. Open engine hood and run engine at about 2,000 rpm for about 2 minutes under no-load.
4. Perform diagnostic test mode II (Self-diagnostic results).
OK or NG
OK ' GO TO 2.
NG ' 1. Repair or replace components as necessary.
2. GO TO 2.

2 CHECK IGNITION TIMING
1. Run engine at about 2,000 rpm for about 2 minutes under no-load.
2. Rev engine (2,000 to 3,000 rpm) two or three times under no-load, then run engine at idle speed.
3. Turn off engine and disconnect throttle position sensor harness connector.
4. Start and rev engine (2,000 - 3,000 rpm) two or three times under no-load, then run at idle speed.
5. Check ignition timing with a timing light.
15°±2° BTDC (in “P” or “N” position)
OK or NG
OK ' GO TO 4.
NG ' GO TO 3.

3 ADJUST IGNITION TIMING
1. Adjust ignition timing by turning distributor after loosening securing bolts.
2. Turn off engine and connect throttle position sensor harness connector to throttle position sensor.
' GO TO 2.


4 CHECK BASE IDLE SPEED
1. Check idle speed.
700±50 rpm (in “P” or “N” position)
OK or NG
OK ' GO TO 6.
NG ' GO TO 5.

5 ADJUST BASE IDLE SPEED
1. Rev engine (2,000 to 3,000 rpm) 2 or 3 times under no-load then run engine at idle speed.
2. Adjust idle speed by turning idle speed adjusting screw.
700±50 rpm (in “P” or “N” position)
' GO TO 6.

6 CHECK TARGET IDLE SPEED
1. Turn off engine and connect throttle position sensor harness connector.
2. Start and rev engine (2,000 to 3,000 rpm) 2 or 3 times under no-load then run at idle speed.
3. Check idle speed.
750±50 rpm (in “P” or “N” position)
OK or NG
OK ' GO TO 9.
NG ' GO TO 7.

7 DETECT MALFUNCTIONING PART
Check the following.
1. Check IACV-AAC valve and replace if necessary.
2. Check IACV-AAC valve harness and repair if necessary.
3. Check ECM function by substituting another known good ECM.
(ECM may be the cause of a problem, but this is rarely the case.)
' GO TO 9.

9 CHECK FRONT HEATED OXYGEN SENSOR LH SIGNAL
1. Run engine at about 2,000 rpm for about 2 minutes under no-load.
2. Set “Left bank front heated oxygen sensor monitor” in the Diagnostic Test Mode II.
3. Make sure that MIL goes on more than 5 times during 10 seconds at 2,000 rpm.
OK or NG
OK ' GO TO 12.
NG (MIL does not blink.) ' GO TO 17.
NG (MIL blinks less than 5 times.)
' 1. Replace front heated oxygen sensor LH.
2. GO TO 10.


10 CHECK FRONT HEATED OXYGEN SENSOR LH SIGNAL
1. Warm engine to normal operating temperature.
2. Run engine at approx. 2000 rpm for approx. 2 minutes under no-load.
3. Set “Left bank front heated oxygen sensor monitor” in the Diagnostic Test Mode II.
4. Make sure that MIL goes on more than 5 times during 10 seconds at 2,000 rpm.
OK or NG
OK ' GO TO 13.
NG ' GO TO 11.

11 DETECT MALFUNCTIONING PART
Check the following.
1. Check fuel pressure regulator.
2. Check mass air flow sensor and its circuit.
3. Check injector and its circuit.
Clean or replace if necessary.
4. Check engine coolant temperature sensor and its circuit.
5. Check ECM function by substituting another known good ECM.
(ECM may be the cause of a problem, but this is rarely the case.)
' GO TO 2.


13 CHECK FRONT HEATED OXYGEN SENSOR RH SIGNAL
1. Set “Right bank front heated oxygen sensor monitor” in the Diagnostic Test Mode II.
2. Make sure that MIL goes on more than 5 times during 10 seconds at 2,000 rpm.
OK or NG
OK ' INSPECTION END
NG (MIL does not blink.) ' GO TO 16.
NG (MIL blinks less than 5 times.)
' 1. Replace front heated oxygen sensor RH.
2. GO TO 14.


14 CHECK FRONT HEATED OXYGEN SENSOR RH SIGNAL
1. Warm engine to normal operating temperature.
2. Run engine at approx. 2000 rpm for approx. 2 minutes under no-load.
3. Set “Right bank front heated oxygen sensor monitor” in the Diagnostic Test Mode II.
4. Make sure that MIL goes on more than 5 times during 10 seconds at 2,000 rpm.
OK or NG
OK ' INSPECTION END
NG ' GO TO 15.

15 DETECT MALFUNCTIONING PART
Check the following.
1. Check fuel pressure regulator.
2. Check mass air flow sensor and its circuit.
3. Check injector and its circuit. Clean or replace if necessary.
4. Check engine coolant temperature sensor and its circuit.
5. Check ECM function by substituting another known good ECM.
(ECM may be the cause of a problem, but this is rarely the case.)
' GO TO 2.
16 CHECK FRONT HEATED OXYGEN SENSOR RH HARNESS
1. Turn off engine and disconnect battery ground cable.
2. Disconnect ECM harness connector.
3. Disconnect front heated oxygen sensor RH harness connector.
4. Check harness continuity between ECM terminal 50 and front heated oxygen sensor RH harness connector.
Continuity should exist.
OK or NG
OK ' 1. Connect ECM harness connector.
2. GO TO 18.
NG ' 1. Repair or replace harness.
2. GO TO 9.

17 CHECK FRONT HEATED OXYGEN SENSOR LH HARNESS
1. Turn off engine and disconnect battery ground cable.
2. Disconnect ECM harness connector.
3. Disconnect front heated oxygen sensor LH harness connector.
4. Check harness continuity between ECM terminal 51 and front heated oxygen sensor LH harness connector.
Continuity should exist.
OK or NG
OK ' 1. Connect ECM harness connector.
2. GO TO 18.
NG ' 1. Repair or replace harness.
2. GO TO 9.

18 PREPARATION FOR “CO” % CHECK
1. Disconnect engine coolant temperature sensor harness connector.
2. Connect a resistor (4.4 kW) between terminals of engine coolant temperature sensor harness connector.
' GO TO 19.

19 CHECK “CO” %
1. Start engine and warm it up until engine coolant temperature indicator points to the middle of gauge.
2. Rev engine (2,000 to 3,000 rpm) two or three times under no-load, then run engine at idle speed.
3. Check “CO” %.
Idle CO: 1.5 - 9%
After checking CO%,
a. Disconnect the resistor from terminals of engine coolant temperature sensor.
b. Connect engine coolant temperature sensor harness connector to engine coolant temperature sensor.
OK or NG
OK ' 1. Replace front heated oxygen sensor LH.
2. GO TO 10.
NG ' GO TO 20.

20 DETECT MALFUNCTIONING PART
Check the following.
1. Connect front heated oxygen sensor harness connectors to front heated oxygen sensors.
2. Check fuel pressure regulator.
3. Check mass air flow sensor and its circuit.
4. Check injector and its circuit.
Clean or replace if necessary.
5. Check engine coolant temperature sensor and its circuit.
6. Check ECM function by substituting another known good ECM.
(ECM may be the cause of a problem, but this is rarely the case.)
' GO TO 2.